When I say win, I mean what type of strategy would you use to counter a proxy war?

For example, 2 parents have a child and then split, the parents don't want to fight each other over various issues regarding the child, so they employ proxies (family and friends) that are used instead.

In this case the victim is the child, as it is difficult to prove/disprove that a proxy is doing something that isn't in the child's best interests or following for instance a court order.